The present invention relates, in general, to semiconductor devices, and in particular to leadframes for power semiconductor devices that permit different bond wire materials within the same package.
Current leadframes for power semiconductor device packages (e.g., TO-218, TO-220, DPAK, D.sup.2 PAK, D.sup.3 PAK) typically are formed or stamped from a ribbon of a single or dual gauge metal material such as copper or a copper alloy. Typically, prior to stamping, all or part of the ribbon material is plated with another metal. After stamping, a typical power semiconductor leadframe comprises a die bond pad and a plurality of leads either connected to the die bond pad or in proximity to it. All or some of the leads include a bond post portion for connecting (e.g., wire bonding) a semiconductor die to the leads.
In higher current power semiconductor packages, manufacturer's often use a large diameter aluminum wire to wire bond a current carrying electrode (e.g., a source electrode on insulated gate field effect transistor (IGFET) devices) on the semiconductor die to a lead. When aluminum wires are used, the bond posts are completely covered with nickel because aluminum does not bond well with copper. In addition, the leads typically are plated with nickel.
When an aluminum wire is used for the current carrying electrode wire bond, manufacturers have to use an aluminum wire to wire bond a control electrode (e.g., a gate electrode in an IGFET device) on the semiconductor die to one of the leads. This is because other bond wire materials such as gold or copper are incompatible with nickel covered bond posts.
Aluminum bond wires for the control electrode typically have a diameter on the order of 0.10 to 0.13 millimeters (mm) (approximately 4 to 5 mils). Using a control electrode bond wire of this diameter results in several limitations. For example, it requires manufacturers to use a large control electrode pad on the semiconductor die in order to accommodate the large diameter control electrode bond wire. This severely limits a manufacturer's ability to reduce die dimensions, which in turn impacts manufacturing costs and design flexibility.
What is needed is a cost effective leadframe structure that permits a manufacturer to use different bond wire materials within the same power semiconductor package.